1. Technical Field
Methods for forming patterns of semiconductor devices are disclosed which can inhibit collapse of the patterns during pattern-forming processes by forming micro-bends in the anti-reflective film thereby increasing the contact area between the photoresist and the anti-reflective film and, at the same time, prevent CD critical dimension) alteration of the photoresist pattern having micro-bends and which double-laminate two anti-reflective films with different refractive indices and light-absorbencies.
2. Description of the Related Art
It is known in microfine pattern-forming process among conventional semiconductor production methods that standing waves generated by optical properties of the lower film layer, that is, a substrate of a photoresist film and/or alteration of thickness of a photosensitive film, reflective notching, and/or CD variation of the photoresist pattern derived from diffracted light and reflective light emitted from substrates occurs. Accordingly, it has been proposed to introduce a layer for reducing the reflection onto the substrate between the substrate and the photoresist by employing materials with excellent light-absorbing ability within a range of wavelengths of exposure light sources. Such a protecting layer being is referred to as an anti-reflective film. Anti-reflective films may be generally classified into inorganic and organic based anti-reflective films based on types of materials to be used.
In recent years, the organic anti-reflective films are predominantly used in microfine pattern-forming processes and a number of the organic anti-reflective films have been proposed.
Meanwhile, if the adhesive ability of the photoresist and the organic anti-reflective film is poor, collapse of the photoresist pattern formed on top of the anti-reflective film may occur. Accordingly, two methods to solve this problem have been proposed. One method is to develop organic anti-reflective films to match with particular photoresists selected to form the desired patterns to thereby the adhesiveness between the photoresist and the anti-reflective film. However, development of novel organic anti-reflective films is expensive and requires lengthy research efforts so that such a strategy may not be cost effective.
Another method for enhancing the adhesiveness between photoresists and anti-reflective films has been to increase the surface contact between the photoresist pattern and the anti-reflective film. But, it is well known that increasing the surface contact is also substantially restricted since the contact area is usually determined by the photoresist pattern CD.
Applicants have found that when an etching process is performed on an organic anti-reflective film after coating the organic anti-reflective film, it can form micro-bends (too small to be observed by SEM) which increase the surface contact area between the organic anti-reflective film and the photoresist pattern when forming photoresist patterns on such micro-bends. Then micro-bends also act to inhibit collapse of the photoresist pattern.
However, such a process may induce differences in the thickness in the anti-reflective film caused by the micro-bends and, due to reflected light from such a difference, generates a CD variation of the photoresist pattern.
Hereinafter, the above problem will be described in detail with reference to the accompanying drawings.
FIG. 1 is a graph illustrating the relation between the reflectivity and the thickness of organic anti-reflective film.
As described above, when the etching process for the organic anti-reflective film is conducted to form the micro-bends, such bends generate variation in thickness from about several xc3x85 to several tens of xc3x85. In particular, as shown in FIG. 1, the reflectivity at the lower limit is equal to or less than 0.5% below the poor level of the reflectivity to be a problem, which means that reflected of light in an amount of 0.5% or less of total amount of light generated by the light source. While this occurs, for example, 70 xc3x85(=7 nm) of thickness difference, it leads to 2.0% of the reflectivity causing a severe reflection so that CD variation of the photoresist patterns results.
Due to such existing problems as described above, it has been still urgently demanded to find improved method for pattern-forming in semiconductor device which can inhibit collapse of patterns by increasing adhesive ability between photoresist pattern and anti-reflective film and, at the same time, prevent CD uniformity of photoresist patterns from being lowered.
Accordingly, methods for forming patterns of semiconductor devices are disclosed which can inhibit collapse of photoresist patterns during pattern-forming processes by forming micro-bends in the anti-reflective film to increase the contact area between the photoresist and the anti-reflective film and, at the same time, prevent CD alteration of the photoresist pattern resulting from the micro-bends by double-laminating two anti-reflective films with different refractive indices and light-absorbencies.
Semiconductor devices produced using the above methods for forming photoresist patterns of a semiconductor device.
The disclosed method for forming a photoresist pattern of a semiconductor device comprises (a) applying a first organic anti-reflective coating composition on a surface of a layer to be etched and conducting a baking process to form a first anti-reflective film; (b) onto the upper portion of the first anti-reflective film, applying a second organic anti-reflective coating composition with a different refractive index and light-absorbency from the first composition and conducting a further baking process to form a second anti-reflective film; (c) performing an etching process of the formed anti-reflective films to form micro-bends thereon; and (d) coating the photoresist above the anti-reflective films with micro-bends, exposing the coated anti-reflective films to a light source and then developing the same to form desirable photoresist patterns.
Using the disclosed method, micro-bends are formed on the anti-reflective film suitable to increase contact area between the anti-reflective film and the photoresist patterns by progressing the etching process, resulting in prevention of the photoresist patterns from collapsing; and producing the anti-reflective film by double-coating two kinds of organic anti-reflective coating compositions with different refractive indices and light-absorbencies so that it can minimize reflective light derived from the difference in thickness in the anti-reflective films by interference of the light (that is, destructive interference), thereby preventing CD alteration problem from the reflective light.
An embodiment of the method for forming patterns of a semiconductor device according to the present invention preferably uses a first coating composition having a refractive index ranging from 1.20 to 2.00 and light absorbency ranging from 0.2 to 0.9 of and the second coating composition having a refractive index ranging from 1.20 to 2.00 and light absorbency ranging from 0.00 to 0.50, respectively. Such a range of light absorbency can provide a final anti-reflective film with preferable light-absorbency thereby efficiently removing the reflection of lower film layer, and greatly reduce reflective light generated due to the differences in thickness of the anti-reflective film by means of the formed first and second anti-reflective films with the preferable refractive indices.
Particularly, with respect to a microfine pattern-forming process using 193 nm ArF light source, DARC-20 (commercial trade name, with a refractive index of 1.64 and light-absorbency to 193 nm light of 0.64) is preferably employed as the first anti-reflective coating composition while as the second anti-reflective coating composition, DARC-21 (commercial trade name, with a refractive index of 1.54 and light-absorbency to 193 nm light of 0.38) or DARC-22 (commercial trade name, with a refractive index of 1.49 a light-absorbency to 193 nm light of 0.33) are preferably applied. Since the coating compositions described above show optimal light-absorbencies and refractive indices to 193 nm light, it is expected that employing such compositions can substantially eliminate the reflective light generated due to the difference in thickness of the anti-reflective films by means of light interference, so that the disclosed method can prevent CD alteration of the film caused by the reflective light and, thereby allowing the final obtained anti-reflective film to have an optimum light-absorbency.
Another disclosed method comprises preparing the first and second anti-reflective films with a preferable thicknesses of about 355 xc3x85 and 1000 xc3x85, respectively. After preparing each of the anti-reflective films having such a thickness, it is under the etching process to produce micro-bends. As a result, the etched first anti-reflective film has a thickness of about 355 xc3x85 while the second film has a thickness of about 1000 xc3x85. Because the interference of light depends on the refractive index and thickness of the respective layer, it is understood that if the first and second films having the above refractive indices maintain those thicknesses. The reflective light generated due to the micro-bends may be minimized by destructive interference of the light so that it maintain uniformity of the photoresist patterns.
In the method for forming patterns of a semiconductor device the present invention, the baking process is preferably conducted at about 150 to about 300xe2x96xa1C. for about 1 to about 5 minutes. Under such conditions, acid is generated from a thermal acid generator to form cross-linkage bonds within the anti-reflective film and, thereby producing the desired anti-reflective film which does not dissolve in the solvent of the photoresist.
Moreover, the baking process can be additionally performed before and/or after the exposure process and preferably in the range of 70 to 200xc2x0 C.
Such a photoresist pattern-forming method can be applied preferably in microfine pattern-forming processes using ArF, KrF, deep-ultraviolet (DUV) including EUV, E-beam, X-ray or ion beam, although they are generally employed in microfine pattern-forming processes using ArF light source.
Still another aspect of the present invention provides a semiconductor device produced using the photoresist pattern-forming method according to the present invention.